Most GRUBS Rubber footwear uses self-insulating INSU-FOAM ULTRAbootie construction which acts as a neutral medium between the wearer and the outside. The bootie is both waterproof and insulating and exceeds the long-term effectiveness of waterproof membranes and lofted insulations. The boots are waterproof to EN ISO 20344: 2004 5.7 standard. FROSTLINE 5.0 is insulated and waterproof with excellent grip made for all day comfort. 5MM INSU-FOAM ULTRA - gives all round foot comfort and insulation. 6mm NITROCELL footbed - provides a soft cushioning for an athletic shoe feel. A million microscopic nitrogen bubbles that insulate the wearer from cold surfaces. UNDERFOOT CHASSIS - give a sure footed platform. HEXZORBtechnology - absorbs heel strike shock for daylong comfort. SUPERDRI lining - is hard wearing wicks moister away from the wearers foot to prevent a sweaty and uncomfortable feel. It is fungus and rot proof so will not smell like cotton-lined boots. TRAX outsole - superior grip on a variety of surfaces the tread is designed to work with the action of the foot COMFORT RATING - -20 Degrees Celsius to +20 Degrees Celsius We recommend purchasing the same UK size as your regular daily footwear such as a trainer. Grubs Boots have a 15mm allowance for a woolblend / thicker sock which also means if you are a half size we recommend sizing down.